Loud-speaker



' June 10, M i-c. HOPKINS 1,763,051

LOUD SP EAKER Original File d Ja'nf5 1926 ESheets-Sheet 1 IlTTTIlllllllll|lllllllllll1jll1l I IINVE T-Q' ATToRNEY Jun 10,11930.

M. c. HOPKINS LOUD SPEAKER Original Filed Jan. 5/1926 5 Shets-Sheet 2ATTORN EY S June 10, 1930. M. c. HOPKINS mun SPEAKER 3 Sheets-Sheet 5Original Filed Jan. 5, 1926 WWII:

. ATTORNEY Patented June 10, 1930 UNITED STATES PATENT OFFICE ms 0.HOPKINS, OF wASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOB TO HOP- KINSMBPOBATION, OF JERSEY CITY, NEW JERSEY, A CORPORATION 01' DELA- WAKE fLOUD-SPEAKEB Application fled January l, 1888, Serial Io. 79,889.Renewed December 24, 11m.

The present invention relates to loud speakers of the type disclosed inmy nding application, Serial No. 77,033, file Dec. 22, 1921. The loudspeaker disclosed in that ap lication .comprises a central relativelylig t'and stifi' tympanum, preferably conical in shape, and asurroundingexternal sound board or resonator having greater mass thanthat of the central diaphragm. The connection between the central tpanum and the external resonator or soun boardis such that the centraltympanum will respond to the relatively high frequencies and-willeflicientl reproduce the hi h tones or sounds,

and the relatively low requencies will be transmitted through saidconnection-to the sound board so that it will respond to the relativelylow frequencies and W111 efficiently reproduce them. he principal objectof this an invention is to provide a loud speaker of the foregoin t pe,the sound board of which is made of in sa wood.

It has been found that a loud speaker of the foregoing type producessuperior results if the sound board be made of balsa wood.

Balsa wood seems to have the requisite properties to improveconsiderably the regenera-' tion of the relatively low frequencies whichare passed on to the sound board for reproao duction. I am not preparedto state exactly what properties of balsa wood are responsible.

for the improved operation of the loud speaker disclosed in thisapplication, but undoubt edly the'soft nature of this type of wood and85 its extreme lightness are contributing factors. Several forms of loudspeakers in which balsa wood may be advantageously employed aredisclosed in the accompanying drawings, in which Fi 1 is a front view ofa loud speaker especia ly designed for use in hotels, theatres, concerthalls and similar places where a large volume of sound is desired; a

Fig. 2 is a side elevation of the speaker shown in Fig. 1;

Fig. 3 is a rear view of the loud speaker shown in Fig. 1;

Fig. 4 is a vertical section taken on the line 4-4 .of Fig. 3;

Fig. 5 is an enlarged detail vertical section of the central portion ofthe loud s aker showing the connection between the central tympanumandthe external sound board;

' Fig. 6 is a front elevation of another type of loud s eaker operatingon the same principle as t at shown in Fig. 1;

Fig. 7 is a top plan view of the loud speaker shown in Fig. 6;

Fig. 8 is a rear elevation shown in Fig. 6; v

Fig. 9 is a vertical section taken on the line 99 of Fig. 8.

Referring first to Figs. 1 to 5 inclusive, the loud speaker shown inthese'figures comprises a central conical tympanum 1 coupled to avibratory resonator or sound board 2 by means of a semi-flexiblecoupling, shown in Fig. 5. The conical tympanum 1 is preferably madeofcover paper out and folded to shape and glued along a radial seam.Near the outer edge of the cone thus formed the paper iscreased and thenfolded up to form a orwardly flaring brim 3 (Fig. 5,). This brimnaturally assumes an angle to the plane ofth e base equal to the anglebetween the radial elements of the cone and that base. The outer edgeportion of the brim 3 is preferably glued to the inner circular edge ofthe resonator or sound board 2. For this purose the inner circular edgeof the sound oard is tapered as shown at 4 and the outer edge portion ofthe brim 3 seats upon and is glued to the tapering surface thus formed.In gluing or cementing the brim to the bev eled edge 4 it is importantthat a part of the brim be left free to form a hinge on which the conemay float. Thus with a brim wide the cemented portion may have a widthof of an inch more or less and the remainder' of the brim may be leftfree to SWll'lg.

The resonator or sound board 2 in accordance with this invention is madeof balsa wood. It can conveniently be made of 3-ply balsa wood as-shownin Fig. 5 with the grain of the inner ply running transverse to thegrain of the two outer plles.

The vibratoryactuating force is applied to the apex of the conicaltympanum by means of a rod or wire 5 which is adapted to be 100 of thespeaker tympanum approximately 17 inches in out-.

side diameter and the reasonator or sound board approximately 4} feet inoutside diameter. The relatively large size of the loud speaker shown inFigs. 1 to 5 inclusive makes it desirable to suspend it by cords orchains which may be attached to any suitable part of the loud speaker,preferably the s ider 8. The loud speaker may be suspended rom theceiling of a room, a bracket or any other supporting device.

The loud speaker shown in Figs. 6 to 9 inclusive is very similar inconstruction to that above described as it comprises a conical tympanum1', a. sounding board or resonator 2, a spider 8 for supporting. thecasing 7 of the electromagnetic actuating mechanism,

and a forwardly flaring brim 3 on the cone which is attached to theinner edge of the sound board in the same manner as explained inconnection with Figs. 1 to 5. The resonator or soundboard 2 of this formof the loud speaker is also made of balsa wood as in the case, of theloud speaker described above. The main difference between the speakershown in Figs. 6 to 9 inclusive and that shown in the first five figuresis that the sound board or resonator 2 is of smaller diameter thanthe-sound board shown in the first five figures. The conical tympanum 1-may or may not be smaller than the conical tympanum of the loud speakerof Figures 1 to 5. The reduction in overall size of the loud speakershown in Figs. 6 to 9 inclusive makes it possible to support the speakeron a table or other horizontal surface and for this reason the soundboard 2' is provided with suitable legs or cross pieces 10 glued orotherwise fastened to the sound board. The sound board may be providedwith an opening 11 to provide a hand grip for moving the loud speakerfrom one place to another. In con.- structing a loud speaker of the typeshown in Figs. 6 to 9 I have found that excellent results are obtainedby making the cone 2 approximately 15 in diameter and the sound boardapproximately 22 in diameter. This makes the transverse width of theannular sound board approximately 3%" but good results may be obtainedby making the sound board of even less width than this or of evengreater width than the sound board shown in Figs. 1 to 5 inclusive.

In both types of speaker the 'central conimediate tones while thesurrounding annular resonator or .-ound board efficiently reproduces thelower or bass notes. By reason of the fact that the sound. board is madeof balsa woodthe reproduction of the lower or bass notes is considerablyimproved. The lower notes are not onl more accuratel reproduced but thetonal quality is conslderably improved, the reproduction being soft andmellow.

- In a loud speaker constructed in accordance with the foregoingdescription, the regenerated or reproduced sound waves are substantiallydirectly proportional both quantitatively and qualitatively to theactuating force and the sound so reproduced retains substantially thesame balanceof high and low tones as the'original sound from which theactuating force'was derived.

In the claims the term diaphragm is used to designate the entirevibratory body including the tympanum and the soundboard. y

I claim:

1. A loud speaker comprising a central I relatively light and stiff tmpanum, an external balsa wood sound board of reater mass than thediaphragm, and a flexible coupling between the two adapted to permit thecentral tympanum to respond to rela-- tively high frequencies andadapted to transmit the relatively low frequencies to the sound board.

2. A loud speaker comprising a central conical tympanum, an externalbalsa wood sound board of greatermass than the tympanum, and a flexiblecoupling between the two adapted to permit the conical tympanum torespond to relatively high frequencies and adapted to transmit therelatively low frequencies to the sound board.

3. A loud speaker comprisin a central conical tympanum, an externalbalsa wood sound board and a connection between the conical tympanum andthe sound board adapted to permit the central tympanum to respondto'relatively high frequencies and adapted to transmit the relativelylow frequencies to the sound board.

4. A loud speaker comprising a central conical tympanum, a balsa woodsound board extending radially beyond the conical tympanum and aconnection between the conical tympanum and the wooden sound boardadapted to permit the conical tympanum to respond to relatively highfrequencies and adapted to transmit the relatively low frethe conicaltympanum, said forwardly flan ing brim portion of the conical tympanuin.being attached to the sound board.

6. A loud speaker comprising a conical tympanum provided with aperipheral cerrugation forming a hinge portion and a balsa wood soundboard ext-ending radially beyond the conical tympanum, said hingeportion being secured to said sound board.

7. A loud speaker comprising a balsa wood soundboard, and a conicaltyn'ipanum flexibly connected thereto so that a portion of the soundboard extends radially beyond the conical tympanum, the flexibleconnection between the conical tympanum and the sound board beingadapted to permit the conical tympanum to respond to relatively highfrequencies and being adapted to transmit the relatively low frequenciesto the sound board;

8. A. loud speaker comprising a central conical tympanum made of paper,an external sound board made of balsa wood, and a lie:-

ible connection between the two adapted to' permit the conical tympanumto respond to relatively high frequencies and adapted to transmit therelatively low frequencies to the sound board'.

9. A loud speaker comprising a balsa wood sound board having a centralopening a conical tympanum mounted in said opening actuating means forthe conical tympanum and means for supporting said actuating meanscomprising a support attached to the sound board and spanning thecentral opening thereof.

10. A loud speaker comprising an annular flat balsa wood sound boardhaving a circular central opening, a conical tympanum having a circularperiphery, said conical tympanuin being mounted in said opening, and aflexible coupling between the conical tympanum and the sound boardadapted to permit the conical tympanum to respond to relatively highfrequencies and adapted to transmit relatively low "frequencies to thesound board.

11. A loud speaker comprising an annular balsa wood sound board having acentral opening the edge portion of which is provided with a taperingseat, and a conical tympanum 'niounted in said opening, said tvmpanumhaving a forwardly flaring frusto-conical brim portion secured to thesound board on said tapering seat.

12. A loud speaker comprising a flat annu- 'lar sound board made ofbalsa wood, said sound board having a central opening the edge portionof which is provided with a tapering seat, and a fibrous conicaltympanum mounted in said opening and having an integral forwardlyprojecting brim portion, a part of said brim portion being attached tothe sound board a t said tapering seat.

13. A loud speaker comprising a .diaphragrn, and means for applyingvibratory energy thereto the portion of said diaphragm where the energyapplied being of relatively small mass and freely responshre to thehigher ia'mpiencies, and said diaphragm havin other portion of greatermass formed oi. balsa wood which is freely responsive to the lowerlrequencics.

14:. A loud speaker comprising a diaphragm having a. sound reproducingrim of bah-a vmod which is freely responsive to the lower frequenciesand a portion of less mass within said rim. which is freely responsiveto the higher frequencies and means for impressing vibratory energy onsaid portion Within the rim.

In testimony whereof I atfix my signature.

MARCUS C. HOPKINS.

